i have a 'dead' sla 12v 7amp that i got in great shape, and when i ran it down doing jb3 tests, it just wont charge up anymore, and its a damn ecocharge
i got a powersonic 12v 12 amp that i have now atht has worked beautifully so far, i think the key w/ some batts is dontlet them deep discharge
ive done that MANY times w/ my eco 6v's, but its not good practice, and because of the deep discharge thing, i beliefve i have a dead battery that i MAY get going w/ a bulk, ie~not smart charger
so if ya dont need to run your batts all the way down, dont
YMMV tho